1. Field of the Invention
The present invention relates to a photographic polyester film and a manufacturing method therefor, and more particularly, to a photographic polyester film exhibiting good adhesiveness between a base film and a photosensitive layer, in which interlayer adhesiveness between a primer layer and a subbing layer can be maintained even if the base film with the primer layer is left for a long time before the subbing layer is formed on the primer layer, and a manufacturing method therefor.
2. Description of the Related Art
A photographic film consists of a hydrophobic base film such as a polyester film and a photosensitive layer formed on the base film. However, separation of the photosensitive layer from the polyester film is frequent during the entire process including development, fixation and washing. This is because the polyester film has strong hydrophobicity while most materials for the photosensitive layer, e.g., gelatin containing silver halide, have strong hydrophilicity, so the adhesiveness between the polyester film and the photosensitive layer is very weak.
Thus, research has been conducted to enhance the adhesiveness between the polyester film and the photosensitive layer. In a conventional method, a polyester film is pre-treated to form a primer layer on at least one surface of the base film, a subbing layer is formed on the primer layer with a natural polymer such as gelatin, and then a photosensitive layer is formed on the subbing layer.
Hereinafter, a conventional method for forming a subbing layer will be explained.
In general, the subbing layer is formed by an off-line method and an in-line method which are both in practical use and can be applied to the following prior art.
U.S. Pat. No. 3,545,972 discloses a method for manufacturing a photographic polyester film with an enhanced interlayer adhesiveness, in which a subbing layer is formed of a terpolymer consisting of alkyl acrylate or alkyl methacrylate, an aliphatic monomer having two or more reactive groups, and itaconic acid, fumaric acid, acrylic acid or methacrylic acid, and a water permeable photosensitive organic colloid is coated on the subbing layer. Also, a water permeable organic colloid material layer without photosensitivity may be formed between the subbing layer and the photosensitive organic colloid layer. An in-line coating method is used in the formation of the subbing layer, a biaxial drawing method in which drawing is performed widthwise after the subbing layer is formed on a lengthwise drawn polyester film.
U.S. Pat. No. 3,874,877 discloses a photographic polyester film having a primer layer which is formed of polyamide-epichlorohydrine resin on the polyester film, and a subbing layer and a photosensitive layer which are formed in sequence on the primer layer. Here, the subbing layer consists of a hydrophilic resin such as a vinyl copolymer with cellulose acetate phthalate, cellulose acetate maleate or maleic anhydride, or gelatin.
U.S. Pat. No. 4,002,802 discloses a method for manufacturing a photographic polyester film in which a primer layer is formed of a copolymer of vinylidene chloride and itaconic acid or an ion exchange resin on a polyester film, and a subbing layer is formed of a polymer resin.
Also, U.S. Pat. Nos. 4,052,528, 4,135,932, 4,167,593, 4,265,946, 4,328,283, 5,510,233 and 5,562,997 disclose a composition for a pre-treatment of a photographic polyester film. In particular, U.S. Pat. No. 4,052,528 discloses a pre-treatment composition containing a tetrapolymer consisting of vinylidene chloride, one selected from the group consisting of alkyl acrylate, alkyl methacrylate, one selected from the group consisting of vinyl acetate and acrylonitrile, a copolymerizable acid and a halogenacetic acid vinyl ester. U.S. Pat. No. 4,135,932 discloses a pre-treatment composition containing a copolymer of styrene and its derivative. U.S. Pat. No. 4,167,593 discloses a pre-treatment composition containing a copolymer of vinylidene chloride, methyl acrylate, itaconic acid and vinyl monomer, U.S. Pat. No. 4,265,946 discloses a pre-treatment composition containing a copolymer of diolefin monomer and vinyl monomer, and U.S. Pat. No. 4,238,283 discloses a pre-treatment composition containing a copolymer of glycidyl acrylate and hydroxy alkyl acrylate with a copolymerizable vinyl monomer. Also, U.S. Pat. No. 5,510,233 discloses a pre-treatment composition containing a substance obtained by curing polyurethane latex with epoxy compound or dichlorotriazine derivative, and U.S. Pat. No. 5,562,997 discloses a pre-treatment composition containing (1) a polymer having carboxyl group at its main chain and a polymer having SO.sub.3 X or PO.sub.3 XY group (where X and Y are independently alkali metal, ammonium or hydrogen), (2) a polymer having carboxyl group at its main chain and SO.sub.3 X or PO.sub.3 XY group at its side chain, or (3) a compound having at least two free hydroxy groups.
In particular, the pre-treatment composition containing vinylidene chloride is the best at enhancing adhesiveness between a polyester base film and a photosensitive layer. However, there is a problem in that the composition can not be applied to an in-line coating method.
That is, when the composition containing vinyllidene chloride is coated on a polyester film by the in-line coating method, the intrinsic physical properties of the composition changes during drawing, so the surface properties of the pre-treated coating layer also change, thereby decreasing the adhesiveness between the base film and a photosensitive layer. To solve this problem, a method of increasing the content of a vinyl or acryl copolymerizable component has been suggested. However, it is not possible to secure a satisfactory interlayer adhesiveness by this method, and it is possible to reuse the film due to vinyllidene chloride.
The second preferred pre-treatment composition, other than vinyllidene chloride, contains acryl polymer. The surface properties of the film formed of this composition change less during drawing and there is less restriction relating to the reusing of the film. However, enhancement in the interlayer adhesiveness is trivial.